This proposal has two specific aims that will add to the understanding of signal processing at the cellular level in the inferior colliculus (IC). The first aim is to investigate whether there is a correlation between neurotransmitter- and receptor- immunoreactivity and cell type as defined by membrane properties and morphology. The second aim is to characterize the synaptic inputs to look for synaptic plasticity in a certain type of IC neuron, the buildup-pauser neuron. By learning about the characteristics that define cell types and extent of synaptic plasticity in the IC we can better understand how incoming information is modified and passed along to other auditory nuclei. Both of these problems will be addressed using intracellular recording in living slices of a rat IC. For the first aim, neurons will be classified according to known action potential firing patterns in current clamp. Morphology will be revealed by biocytin and tissue will be immunostained for neurotransmitter- or receptor- reactivity. Thus, information about action potential firing patterns, morphology and immunohisochemistry will be collected for the same IC neuron. It is expected that neurotransmitter and receptor reactivity will correlate with action potential firing patterns and morphology. Because it receives so much information, synaptic patterns to neurons of the IC are complex. In the second aim fibers of the lateral lemniscus or commisure of the IC will be stimulated with an extracellular electrode to drive synaptic inputs. First I will, using any information gained with immunohistochemistry in the first aim as a guide. Pharmacologically characterize the synaptic inputs to buildup-pauser neurons. GABA and glycine are predicted to be important since buildup-pauser neurons are affected by hyperpolarization. Then I will look for the evidence of synaptic plasticity on buildup-pauser neurons. The prediction that, tetanic stimulation buildup-pauser neurons will show an increase in synaptic weight.